This disclosure is directed to a method for manufacturing polycarbonates.
Aromatic polycarbonates have been widely adopted for use as engineering plastics in many fields because of their excellent mechanical properties such as high impact resistance, heat resistance, transparency, and the like.
Polycarbonates can be manufactured by reacting an aromatic dihydroxy compound with a carbonic acid diester in the presence of a polymerization catalyst. For example, the method of making an aromatic polycarbonate generally comprises an ester interchange reaction (melt polymerization method) between an aromatic dihydroxy compound and a carbonic acid diester using an alkali metal salt as the catalyst. It is noted that this method of manufacturing aromatic polycarbonates has attracted recent attention because it is inexpensive and does not employ toxic substances such as phosgene and methylene chloride. As such, this method is more advantageous from a health and environmental perspective compared to other methods employing, for example, phosgene and methylene chloride.
Separation and reuse of byproducts and recyclable components from a polymerization reaction is important, if a method to prepare polycarbonates is to be economically viable and environmentally safe. In particular, when a reactant like diphenyl carbonate is separated in the polymerization reaction, it is desirable that a reusable form of the reactant be separated and recycled efficiently.